UV radiation can be applied to many fields, such as UV sterilization, UV physiotherapy, UV fluorescent analysis and investigation, UV exposure of photolithography and so on. However, devastating effects of UV radiation may be very dangerous in some cases. For example, cultural relics, paintings and calligraphy works, rubber and plastics will undergo an accelerated aging process under a prolonged exposure to UV irradiation. Moreover, UV radiation may also have devastating effects on eyes, skins, plants and so on. It is very important therefore to be able to detect and determine the intensity and amount of UV radiation.
Gallium nitride (hereinafter referred to as “GaN”) material possesses characteristics of having wide energy gap, high voltage resistance and high temperature resistance and so on, and can be used in the development of UV detecting devices. The UV detecting devices made of GaN can be used in different kinds of environment and for different industrial applications, such as measuring the amount of UV radiation for fire detection, biological examination, air pollution detection and so on.
In general, the UV detector is fabricated by forming GaN Schottky junctions on a GaN thin film grown by Molecular Beam Epitaxy (hereinafter referred to as “MBE”) or metalorganic chemical vapor deposition (MOCVD). The conventional UV detector only comprises a high temperature Aluminum Nitride (hereinafter referred to as “AlN”) buffer layer interposed between a sapphire substrate and a GaN epitaxial layer. The reliability and lifetime of such configured UV detector is usually unsatisfactory and the accuracy thereof decreases significantly after a prolonged exposure to high intensity UV irradiation.
U.S. Pat. No. 5,677,538 discloses an UV detector consisting of a metal-semiconductor-metal structure (i.e. two back-to-back Schottky junctions) which requires application of a bias during normal operation. For the detector, UV detection is performed in the semiconductor material located between the two interdigitated Schottky junctions. The two Schottky junctions are formed by the deposition of a thick metal layer on the GaN thin films. In addition, materials of the detector are fabricated by using an Electron Cyclotron Resonance (hereinafter referred to as “ECR”) plasma source. Most importantly, the GaN epitaxial layer of the detector is grown on a single buffer layer. A disadvantage of the UV detector with such structure is in that its UV detecting performance will gradually degrade with elapse of time and also a voltage bias is required for the operation of the device.
Therefore, it is required to provide an UV detector which is stable and reliable, and has high UV radiation hardness.